This invention relates generally to fluid pressure regulators and more particularly to valves for fluid pressure regulation having resistance to static pressure creep.
A fluid handling system typically includes a device to regulate fluid pressure in the system. The fluid is supplied at a given pressure, usually higher than that desired at the system output ports. It is the function of the regulator device to reduce the fluid pressure to the desired level and to maintain it at that level regardless of variations in downstream flow demand or in supply pressure.
A common single-stage regulator has a fluid supply inlet chamber at the exit of which is a variable orifice valve having an annular seat and a spring biased ball, cone, or other closure element. The proximity of the closure element to the seat is controlled by a valve stem connected to a diaphragm downstream of the valve. The pressure drop of the fluid as it passes through the valve depends upon the size of the valve orifice which is determined by the proximity of the valve closure element to the valve seat.
Downstream from the inlet chamber and valve is the diaphragm chamber, one wall of which consists of a diaphragm whose stiffness is adjustably controlled by a screw adjustable spring which biases the diaphragm toward the diaphragm chamber. The exit from the diaphragm chamber is the service outlet of the regulator.
At any given setting of the diaphragm spring adjustment, the diaphragm assumes a position. When pressurized fluid is admitted to the chamber through the valve, the fluid exerts a force on the diaphragm counter to that exerted by the spring. The resulting displacement of the diaphragm causes a decrease in the valve orifice size as a result of withdrawal of the valve stem and the consequent closer approach of the valve closure element to the valve seat. This increases the pressure drop through the valve which causes the diaphragm to advance, thereby further opening the valve. These counterbalancing forces quickly establish an equilibrium which will obtain during steady flow, so long as the spring adjustment remains unchanged.
In most manufacturing operations there are periods of shut-down, during which the service line fluid flow is discontinued. At such times, there is a possibility of regulator creep which can result in excessive fluid pressure in service lines.
Regulator creep is usually attributable to failure of the valve closure element to properly close against the valve seat due to distortion of the seat or closure element or, infrequently, a dirty or corroded seat or element.
Seat distortion is usually due to thermal or mechanical stresses introduced during assembly of the regulator, by brazing the seat in its housing, by torquing the housing into the regulator body, or by a combination of these and other stress inducing activities. Even a seat which is clamped in metal to metal contact and which has a groove and "O" ring seal with the housing is subject to mechanically induced distortions.
Lapping, rethreading, and other superfinishing techniques are commonly employed to prevent assembly distortion. In spite of these efforts, a significant fraction of regulators must be reworked due to such distortions, and some valve assemblies must be scrapped.
In addition to the cost of rework and scrap in manufacturing of the regulators, if a regulator undergoes static pressure creep, it may cause damage to delicate fluid operated systems.
The foregoing illustrates limitations known to exist in present fluid pressure regulator valves. Thus, it is apparent that it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.